I would love to see two things in Pharo 5:
1) Fix for mouse scrolling (at least on Mac OS X, though I think it does the same on Linux etc) in the class pane. While mouse-scrolling (either via a mouse wheel or two-finger scrolling on the touchpad) through the classes, the focus frequently and erratically jumps to the package pane, and the package pane starts scrolling instead. The focus also sometimes jumps when you reach the end of the class list (and, again, the package pane starts scrolling instead).
2) A button in the debugger that copies the error message to the clipboard (you can sort of do it currently by editing the title of the error window, but that's really awkward).